Joachim has no problem with sunlight at all! Omegafriends vampires are kind of a mixed bag there in general. In Joachim's case, I attribute it to the Valentines being a family of genetic vampires with centuries and centuries of weird magical ritual history.

As for hamon, it's not inconceivable that he's run into it in his travels before but he's also pretty single-minded so whether he knows everything it does is another thing all together. I'll think about it and work out what would be the most entertaining.